1. Field of the Invention
The present invention relates to the viewing of data associated with optical links and more particularly to the viewing and monitoring of data associated with the optical links during the construction, restoration and maintenance of such optical links used in communication systems to determine and confirm the proper operation of the optical links.
2. Description of the Related Art
Communication systems many times use optical links to provide communication services to users by conveying communication signals between various equipment within the system. An optical link is a communication medium through which optical communication signals (hereinafter "optical signals") representing for example data, video, audio and other types of information are conveyed. Communication system providers typically own the optical links and associated equipment connected to such links. FIG. 1 depicts an exemplary communication system 100 that uses optical links to convey optical signals between a central office and a customer site. A central office typically contains equipment owned and operated by a system provider where such equipment transmits and receives various communication signals including communication signals destined for customers or received from customers. For the sake of clarity, only one customer site is shown connected to central office equipment. It is possible for an actual communication system to contain hundreds or even thousands of customer sites and various equipment sites positioned throughout the communication system.
Communication system 100 comprises system provider equipment and customer equipment, i.e., equipment owned and controlled by the system provider and the customer respectively. Demarcation line 110 is a symbolic representation of a boundary distinguishing between user equipment and system equipment. It is possible for demarcation line 110 to represent equipment which couple system provider equipment to customer equipment. For example, demarcation line 110 can be some type of enclosure, e.g., a network interface unit (not shown), within which optical links from the communication system terminate and are coupled to optical links from the customer which also terminate within the network interface unit. The network interface unit may be located at the customer site or nearby the customer site.
Transmitter 102 launches optical signals to the customer equipment via optical links 106 and 107. Receiver 104 receives optical signals from the customer equipment via optical links 108 and 109. At the customer site, optical signals are received and transmitted by receiver 112 and transmitter 114 respectively. Optical links 107 and 109, which are owned and controlled by the customer, are commonly referred to as local links. Typically, at the customer site and at the central office, the received optical signals are converted to electrical signals that are processed by electronic circuitry (not shown). Optical links 106 and 108 will hereinafter be referred to as system optical links.
During construction of communication systems such as the one depicted in FIG. 1, the performance and optical characteristics of optical links are monitored by a craftsperson under the employ of the service provider to confirm the operation of the optical links or determine if any problems exist within the optical links and the location of such problems. Craftspersons also inspect optical links of existing communication systems particularly after said links have undergone some type of reparation. Typically, at a location (116) (e.g., manhole, remote terminal) between a customer site and the central office, a craftsperson makes the necessary reparations or makes the appropriate connections (e.g., splicing) of optical fibers.
An optical communication link such as system optical link 106 or 108 comprises at least one optical cable having a plurality of individual optical fibers. Each optical fiber within the optical cable is carefully spliced using well known standard techniques. During the construction of a system optical communication link (e.g., links 106, 108), a craftsperson typically has to splice hundreds of optical fibers at each of a plurality of locations along the optical link. After each or a group of fibers have been connected (or spliced) at a location, the craftsperson has to confirm that the spliced fibers at that location (e.g., 116) are operating in accordance with design requirements of the communication system. In order to test the spliced fibers, Optical Time Domain Reflectometer (OTDR) 122, located at the central office, launches optical signals through the link being constructed (or repaired) in order to confirm the proper operation of the spliced fibers of the optical link. An OTDR is an instrument which launches optical signals through optical fibers and detects portions of the signal backscattered by the optical fiber. The OTDR generates data characterizing the optical signals based on the backscattered portions. Thus, typically for optical signals launched through an optical fiber, there exist corresponding backscattered portions of the signals which can be detected at the launch point or at some other point along the fiber. Based on the characteristics of the detected backscattered portions, OTDR 118 allows a properly trained craftsperson to determine the functionality or operability of the particular optical link being inspected and/or the location of any problems in the optical link.
FIG. 2 depicts a chart (10) of the amplitude of backscattered portions versus distance. Chart 10 is representative of the type of data generated by OTDR 118 that allow a craftsperson to confirm the proper operation of an optical fiber and/or the location of any problems within the fiber. The distance is measured from the OTDR to various points along an optical fiber. As the distance increases the amplitude of the backscattered portions decreases. At certain points along the optical fiber there is a sharp drop (e.g., 14) in amplitude of the backscattered portions which may be due to, for example, damage in the optical fiber at that location. At other points there may be a sharp and abrupt rise (e.g., 16) in the amplitude of the backscattered portions which may be due to the presence of a discontinuity in the optical fiber path resulting from a connector that couples sections of an optical fiber. Depending on the particular data generation capacity of OTDR 118, thousands (8,000; 16,000 or 32,000) of data values points are calculated in order to create chart 10. OTDR 118 may have a visual display of chart 10 and also may provide a printout of the calculated points. A properly trained craftsperson is able to review and analyze chart 10 to determine whether the fibers within an optical link are operating properly and therefore whether the optical link is operating properly. Proper operation of the optical links of a communication system is defined by the system provider or can be based on a well accepted standard that establishes various criteria that must be met by the data gathered by the test equipment (e.g., OTDR 118). The craftsperson can also monitor the optical links of a communication system, i.e., confirming that the links are operating within bounds set by the system provider or within bounds defined by a well known standard.
Thus, for example, referring to FIG. 1, a craftsperson may be inspecting or testing optical link 106 at location 116 to determine whether a particular fiber or all of the fibers of system optical link 106 are operating properly. OTDR 118 thus can launch an optical signal or a group of optical signals through one or more fibers of optical link 122 and onto system optical link 106 which is coupled to optical link 122 at some point nearby the central office or at the central office itself. For the inspection or testing of system optical link 108, OTDR 118 would launch a signal through one or more fibers of optical link 120 and onto system optical link 108 also coupled at some point nearby the central office or at the central office itself.
The testing of spliced fibers is typically done by two craftspersons in accordance with the following procedure: a first craftsperson ("field craftsperson") constructing or repairing an optical link at a location (e.g., 116) is in communication with a second craftsperson ("central office craftsperson") at the central office. After making several connections (or splices), the field craftsperson instructs the central office craftsperson to operate OTDR 118 causing optical signals to be launched through the optical link within which the spliced (or repaired) optical fibers are located. OTDR 118 is further operated so that it detects the backscattered portions of the launched signals and generates data in the form of chart 10 of FIG. 2. Presumably, the central office craftsperson is able to review, analyze and interpret the chart generated by OTDR 118 to determine whether the spliced fibers are operating properly. The field craftsperson can splice another group of fibers and in the same manner confirm their proper operation with the central office craftsperson. The process discussed above is repeated until all of the optical fibers at one location have been properly connected or repaired. The field craftsperson then moves to another location along the optical link and repeats the entire procedure. During construction or repair of an optical link of a certain length, the field craftsperson typically has to make repairs or connections at several locations along the optical link to ensure the proper operation of the entire optical link.
The process of constructing or inspecting an optical link is thus clearly time consuming and costly. As discussed above, this process requires the skills and expertise of two craftspersons which further adds to the cost of construction and/or reparations of optical links. In order to avoid the use of two craftspersons for inspecting, repairing and/or constructing an optical link, the field craftsperson, after splicing a group of fibers, would have to return to the central office to operate OTDR 118 to determine whether the spliced optical fibers within the optical link are operating properly. As there may be hundreds of optical fibers to be connected (or spliced) at location 116, the field craftsperson would have to make several roundtrips between location 116 and the central office. Location 116 can be miles away from the central office and thus the use of only one craftsperson to construct and/or repair an optical link in such a manner is clearly impractical.
Therefore, there is a need to reduce the costs associated with using test equipment to inspect and confirm the proper operation of an optical link of a communication system during the construction, restoration and maintenance of such a system.